1. Field of the Invention
The present invention relates to a device for analyzing electrical signals from a heart of the type having a measurement unit for generating a measurement signal related to the electrical activity of the heart and an evaluation unit for identifying abnormal conditions in the heart on the basis of the measurement signal.
The present invention also relates to a heart stimulator, embodying such an analysis device, for detecting and treating tachyarrhythmias in a heart.
2. Description of the Prior Art
In the diagnosis and treatment of patients with various abnormalities in cardiac function, the ability to make reliable distinctions between normal and abnormal events in the heart is important. The heart's intrinsic signals, i.e. the ECG signals, have long been used for distinguishing between normal and various abnormal conditions.
The ability to distinguish normal heart conditions from abnormal conditions is especially important in the case of tachyarrhythmias. Examination of the heart rate alone is not enough for a reliable determination of whether a tachyarrhythmia is present. Some hearts manage to operate normally at rates up to about 200 beats a minute, whereas other hearts develop unstable tachyarrhythmias at rates of only 100-120 a minute. Thus the use of parameters other than the heart rate is necessary for establishing whether a heart is afflicted by unstable tachyarrhythmia.
Retrograde conduction from a ventricle to an atrium is another cardiac defect for which identification is important. Retrograde conduction impairs the heart's pumping capacity and can trigger PMT's (pacemaker mediated tachycardia), i.e. a tachycardia evoked and sustained by a heart stimulator.